SPM Chemistry (KSSM) Paper 1

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8.1.1 Alloys and Their Importance

SPM Chemistry (KSSM) Paper 1 8.1 Alloys and Their Importance 8.1.1 Alloys and Their Importance
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Alloys

  1. An alloy is a mixture of two or more metals mixed in a certain percentage.
  2. Most pure metals are weak and soft. The properties of pure metals can be improved by making them into alloys.
  3. Alloys are made to
    1. increase the hardness of metals.
      Example:
      Magnalium is made from aluminium and magnesium to improve the hardness of the pure metals but at the same time, maintaining their lightness.
    2. prevent the corrosion of metals.
      Stainless steel which can resist rusting is made by adding carbon, chromium and nickel to iron.
    3. improve the beauty and lustre of metals.
      Copper and antimony added to tin produce pewter, which is used to make decorative items.
Q & A

Q: Explain why alloy of copper is harder than pure copper?
A:

  1. In alloys of copper, foreign atoms are present. 
  2. The impurities can prevent the layers of copper atoms slide over each other, thus making the metals harder, less malleable and ductile.
(Pure metal – Atoms can slide over each other easily)
(Alloy – The presence of foreign atoms prevent the atoms of metal slide over each other)
 

Copper Based Alloys

  1. Examples of copper-base alloy are
    1. Cupro-nickel
    2. Bronze
    3. Brass
  2. Most copper base alloy has a shiny surface

Cupro-nickel

Component: Cu 75%, Ni 25%
 
Applications: Coins

Bronze

Component: Cu 90%, Sn 10%
 
Applications: Decorative items, medals, artwork, pots and pans
 
Brass
Component: Cu 70%, Zn 30%
 

Applications: Decorative items, electrical appliances, musical instruments, bell, nails, screw, pots

 

Iron Based Alloys

  1. Examples of iron base alloy are
    1. steel
    2. stainless steel
    3. manganese steel
  2. The iron base alloys are usually very hard

Steel 

Component: Fe 99%, C 1%

Applications: Vehicles, ships, bridges, buildings

Stainless steel

Component: Fe73%, Cr 18%, Ni 8%, C 1%

Applications: Kitchen appliances, watches, machine parts, knives, forks, spoons

Manganese steel

Component: Fe 85%, Mn 13.8%, C 1.2%

Applications: Helmet, spring

 

Aluminium Bases Alloys

  1. Examples of aluminium base alloy are
    1. Duralumin
    2. Magnalium
  2. Aluminium has low density, hence the density of aluminium base alloy is also low.

Duralumin

Component: Al 95%, Cu 4%, Mg 1%

Applications: Aeroplane parts, electric cables, racing bicycles

Magnalium

Component: Al 70%, Mg 30%

Applications: Tyre rim of racing cars, the skeletal body of aeroplanes

 
 

Tin Based Alloys

  1. Examples of tin base alloy are
    1. pewter
    2. solder
  2. Most tin base alloy has a shiny surface and low melting point.

Pewter

Component: Sn 91%, Sb 7%, Cu 2%

Applications: Decorative items, souvenirs

 

Solder

Component: Sn 50%, Pb 50%

Applications: Welding and soldering work

（Welding）
(Soldering)
 
 
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